Type 1 poliovirus RNA is being sequenced to obtain 5'-proximal structures potentially involved in the initiation of protein synthesis in vivo and in vitro. These data are being developed by direct RNA sequencing methods, using 5'-labeled molecules, and by analysis of RNA fragments protected from RNase action after formation of initiation complexes. Together these two approaches will yield information about the structure and location of the rbiosomal binding site in poliovirus mRNA, a non-capped eucaryotic messenger. In other experiments, poliovirus RNA replication is being studied using mutant of poliovirus type 1, tsB9. An unusual RNA species synthesized at 39 degrees C by tsB9 is being characterized. Preliminary data indicates that the production of mature 35S virion RNA is imparied at 39 degrees C in tsB9, and that a large RNA structure is produced which has both single-stranded and double-stranded properties. The nature of the temperature sensitive function is under investigation.